Throughout the business world, multi-color electrophotographic (EP) imaging systems are extensively used for image reproduction. To effect image reproduction, one type of multi-color electrophotographic imaging system employs a photoconductor, such as an endless belt having an organic photoreceptor coating thereon. In this type of multi-color electrophotographic imaging system, latent images, representative of a plurality of different color separation images, are formed in an imaging region of the moving photoconductor belt. The color separation images together define an overall multi-color image. The color separation images may define, for example, yellow, magenta, cyan, and black components that, upon subtractive combination on output media, produce a visible representation of the multi-color image. Prior to an imaging cycle, a uniform charge is applied to the organic photoreceptor coating of the endless belt. Each of the latent images, defining the color separation images, is formed by scanning a modulated laser beam across the moving photoconductor belt to selectively discharge the organic photoreceptor coating of the belt in an image-wise pattern. Appropriately colored developers are applied to the organic photoreceptor coating of the belt after each latent image is formed to develop the latent images. The resulting color separation images ultimately are transferred to the output media to form the finished multi-color image.
In some multi-color electrophotographic imaging systems, the latent images are formed and developed on top of one another in a common imaging region of the photoconductor belt. The latent images can be formed and developed in multiple passes of the photoconductor belt around a continuous transport path. Preferably, the latent images are formed and developed in a single pass of the photoconductor belt around the continuos transport path, because a single pass system enables multi-color images to be assembled at extremely high speeds.
An example of an electrophotographic imaging system configured to assemble a multi-color image in a single pass of a photoconductor belt is disclosed in copending and commonly assigned U.S. patent application Ser. No. 08/537,296 to Kellie et al., filed Sep. 29, 1995, and entitled "METHOD AND APPARATUS FOR PRODUCING A MULTI-COLORED IMAGE IN AN ELECTROPHOTOGRAPHIC SYSTEM".
In an electrophotographic imaging system as described above, the latent images must be formed in precise registration with one another to produce a high quality image. In imaging systems incorporating an endless photoconductor belt, precise registration can be difficult due to deviation of the photoconductor belt from its centered, continuous transport path in a direction perpendicular to the transport path. Specifically, the endless photoconductor belt can undergo side-to-side movement during travel (i.e., conventionally referred to as "belt walking"). The imaging region in which the latent images are formed is fixed relative to the edge of the photoconductor belt. In addition, the scanning beam used to form each latent image in the imaging region is fixed relative to a start-of-scan coordinate. The side-to-side movement of the photoconductor belt can cause movement of the imaging region relative to the start-of-scan coordinate. As a result, misregistration can occur between different scan lines and between different latent images. This misregistration can significantly degrade image quality. In particular, this misregistration can produce visible artifacts in the final multi-color image upon transfer of the misregistered color separation images to the output media.
To eliminate this misregistration, multi-color electrophotographic imaging systems typically employ a registration system that includes a belt steering mechanism. The belt steering mechanism moves the endless photoconductor belt to correct for deviation (i.e., side-to-side movement) of the belt from a desired, centered, continuous transport belt path. The belt steering mechanism generally corrects the side-to-side movement of the endless photoconductor belt by continuously realigning the moving belt to its desired, centered, continuous transport belt path. Prior belt steering mechanisms often have proven to be ineffective, cost-prohibitive, space-prohibitive, or a combination thereof. Typically, these prior belt steering mechanisms have been of complex designs employing a large number of system components. As a result of this design complexity and the large number of system components, the overall reliability of these prior belt steering mechanisms, and thereby the reliability of the multi-color electrophotographic imaging systems employing these prior belt steering mechanisms, has been undesirably diminished.
There is a need for an improved belt steering mechanism for a registration system of a multi-color electrophotographic imaging system. In particular, there is a need for a belt steering mechanism that moves the endless organic photoconductor belt of the imaging system to correct for deviation (i.e., side-to-side movement) of the belt from a desired, centered, continuous transport belt path. By continuously realigning the moving belt to its desired, centered, continuous transport belt path, the belt steering mechanism significantly improves image quality by substantially eliminating misregistration between different scan lines and different latent images that can produce visible artifacts in the final multi-color image on the output media. In addition, the belt steering mechanism should provide these features while being of a reliable, non-complex design so as to be relatively easy and inexpensive to manufacture.